GNGTS 2013 - Atti del 32° Convegno Nazionale

SITE EFFECTS IN THE EASTERN PO PLAIN BY MEAN OF WEAK AND STRONG EARTHQUAKES C. Barnaba, G. Laurenzano, L. Moratto, A. Vuan, M. Romanelli, D. Pesaresi, M. Plasencia Linares, E. Priolo OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale), Centro di Ricerche Sismologiche, Trieste and Udine, Italy Introduction. We present the activities carried out within the S2 2012-2013 Project, funded in the frame of DPC-INGV Agreement, that concerns the mid-long term Seismic Hazard Assessment in Italy on two priority areas, the Po Plain and the Southern Italy. The Po Valley, an area hitherto considered of low seismological interest, has attracted the attention of the seismological community following the events of May 20, 2012. The day after the main shock that stuck eastern Emilia in 2012, the OGS - Istituto Nazionale di Oceanografia e di Geofisica Sperimentale deployed a temporary seismographic network in the Ferrara area. All the investigated locations were set on soft soils. The large amount of collected data allowed comparison between observed PGA and theoretical predictions, ShakeMaps and attenuation laws, but the lack of a reference site during the 2012 recordings did not allow for estimating the amplification factor. In order to accomplish this task, in February 2013, a new 5 stations recording array acquired data at four of the 2012 network sites and at the Casaglia reference site, north of Ferrara, where a borehole Very Broad-Band station is coupled with a mid-period sensor at the surface. This borehole reference station made possible the estimation of site amplification of the 2013 array sites. The reference methods allowed an easier identification of the resonance frequency, which peaks appear sharper than what displayed by single- station methods (both H/V on ambient noise and earthquakes), and relative soil amplification. A large amount of original seismological data has been recorded in a poorly instrumented Fig. 1 – OGS Temporary Network deployed in Ferrara area. Site OG010 is set at the top of the borehole hosting the FERB station. Site OG012 is very close OG002. 179 GNGTS 2013 S essione 2.2